Flame heating of metal castings to reduce shrinkage cavities



Feb. 4, 1958 E. FhkuazmsKl 2,821,760 FLAME HEATING OF METAL CASTINGS TO REDUCE Sl-IRINKAGE C A VITIES Filed Dec. 24, 1956-;

INVENTOR EDWARD F.KURZ|NSKI I; f I y 'ATTORN-EY United States Patent""() munuottgsnnmxncn CAgVITlE S Edwa d 1 K t inskirc a f dtN -tas i a rswtl n yn .l i fi w satiawass rwa l s q -Nsw q kg n a Y t s ha -she rlsaa n t qt swaps WW 129th s ss t lss an as tisaihavin ase ue-i gested. However, prior tolthe presentjnvent ion number a isssl s asasiaat rnt s s sa -ihssti s smahsi employed on a commefcial s eale. i

Ca s l s- 1 1 i a is i ama sss isa shsat n iw t ai s i i In -.3. h lls s asst as ihsitt ts s t a asl s tmalt he wate c lin of 'a-bufner is' undesirable for s evera l reasons. If ,a le ai Q -Pat i th W nst as m a fl ge-m --,si .sti ass 2 t eat e ishsrss q -lss sinawatsr ins the molten metal, and the hofrefractories,yvhieh,. are,em ployed. Water-cooling also creates an undesirable complication of equipment because-two additional conduits for water-mustbe used -Moreover;in'cold weather water in the conduits may freeze when the apparatus is out of uses reduc ng s hrinkage ca In accordance with gthe present invention c there is pro Yi ta e' ss f amas n a solid me castle W1 s.) is? .substantiallyafree from a .shrinkage cavity by pour ng the molten metal-into a mold to form a casting, positioning a gas burner nozzle above the top surface of the casting, ande'applying from'ithev nozzlei against [the top surface anr:;oxy-fuel gas; flame 1ofnthe1=blow1off type to lkeep the topmofethetcasting rnolten -while the zrest of.:the .metal solidifies; A hlow=offr-:type f-.; fla'me is produced :when the oxyn-fual;gasnmixtureitstartsto;burn at-atpoint spaced fromuthe, face .of thesburner nozzle rather thanright at the cfacetasiwithmonyentional flames.

-3IThe tblQW-gOE oxy.fue1;,gasflame used {in-my process iszrfqrmeduby'lso.correlating the ratiolof oxygeneto fuel gastin the combustible-mixture with: theidischarge velocity of zthe. zmixture cthat Lthe =flame starts to :burn at aipoint spaced ofi the face of the burner nozzle, Itsccombu stion sometimes. must be maintained :by.;.the ignitingeffect of someiadditional heating .agency; such as .the heat ofl theh incandescent metal casting itself. For example, when the gas velocity is 500 feet per.- ,second :the flame will not burn in the free atmosphere, but requires the igniting efiect of a hot body to keep it burning. The point at which the flame starts to burn varies dependentlupgn th velocity f th s lss bl m tu l t s sl st a be w en he nozzle and the top of the metal casting. l Jn tsome instances the flame has beenspaced; inch from the nozzle faee; "and in oter a spacing has occurredv when? blow-off flame-is employed in, themanner dcseribed "in the preceding paragraph, the burner is subjected principally tor-the heat 'emanating from the metal casting ..t

2,821,760 Patented Feb. 51, 1958 2 burning at the 'face-ofthe nozzle. Consequently it has been-found feasible to employ a burner without a watercooling-system when-using a blow-off'flame.

To produce the "blow-offtype of flame whichnis employed in myovel process, the oxy-fuel gas mixture shouldfiow at acalc'ulated discharge velocity (quantity of gas flowing/total area of orifice greater than 2.00 feet per second as it leaves the burner nozzle, and the ratio of oxygen :to;fue1"gas in the mixture should. be maintained betyveen-1,31a11d-L8 to 1. A dischargevvelocity of abhutfiGOffeet per secondj'h'as been;found advantageous. velocities in 'excessof 1000, feet per second are not desiz l 'Byusing the process described above it has been'found possible to reduqefilge olumeof metal.,require'd in the rt Pi r t 1 fiQWn t of th i q ol m hil m aintaining the maim b'ody. of the ingot sound and free a hfl s s cavit e Specific ways of employing the principles ofthejinvention will be described in detail below with reference t haassamp nyi d wing lwhsrs m T 3 8 1 "a Per pe v w hq n ta inggt .motd filled with molten steelfibeing treated;by the process of the invention;

Fig. 2 is an enlarged avertical sectional view of the 1. 2am and par q lhl vbw f l 1Q I -i g-- 1 Pi is an elevationalaview.of thec-bur ner as seen 1ow., niEig-. ;.and v is; pei'spe'stivst l par al bm se l wavand n sectigmof another type of casting v beingtreated hY-Jhama ss ptth ia s t m-- vA l svt 31s Bi, 1 t m-inse .sm s -l isa uia men sectional seismi -1min: ha in aan intg raLannu-mr cat liarq sis -i thlana t E11 a ihssafi ls wi h mqlte is't s 4 9a st WiF Wt Q-hQ -QQM After filling the mold a burner 19 has been p laced ip position with its burner noz z1e-; ;21 above the aperture 16 and the top surface of the casting 15. immediately after positioning the burner 19above;the casting a fuel gas such as -naturall-gas "(whichis predominantly-methane) is supplied to a gas mixerbody 23 through=-a supply eon: duit 25- which is provided with anadjustable automatie' pressureg 'fig ltitorflfi simultaneonslydheflowof oxygen iscommenced to-the mixer -body 2-3 through a :supply conduit 29 *having'therein an adjustable automatic pressure regulator 31." EFh'e two gases mixintimatelytogether within thebpdy- 23 and the resulting combustible mix ture passes through-the burner to the nozzle "21; from which it is discharged through a pluralityof ports -33 against the casting 15. The rnixer body 23 may include an .ssnt at ena son rust saz a .iswsl ulsaq n in Umpir s s tstnpl a shown and sssr hss iin t t d S atqsP tsm 2942 4 1- Ih .pt s iati 9 the oxy en o ti ts saw int e 99m: v t bl mix ur .i d ermin d b a us n .theisstti s o the Prsssut r ula q ,27a d 31: Th 11 92 vel c tyiro V pip e. 35,'j the street l. "31 threaLdc-vclfoverthe frdnnend ith? Pi th st eet 1- an hangs th i harge stificss .3. d i led the -n 11h; l ?tb 3 arrangemen an ncl na o lot th -sits? charge orifices 33 can be varied as desired to suit the type of casting being treated, within the scope of the invention. The particular nozzle shown in Figs. 1 and 2 is provided with four orifices arranged as the corners of a square and having their axes diverging downwardly and outwardly from one another so as to direct the flames toward the periphery of the casting 15.

Partially covering the top of the casting 15, as by the annular cover 14, reduces gas consumption considerably over the amount consumed when no cover is used, the saving in gas being as much as 50% in some instances.

In a modified form of apparatus, as shown in Fig. 4, a long and narrow casting 41 is treated with two groups of blow-01f flames 43 and 45 projected simultaneously from a pair of nozzles 47 and 49 connected to a single pipe 51 which is supplied with a combustible mixture from a mixer body (not shown) similar to the mixer body 23 shown in Fig. l.

Several specific examples of how the process of the invention has been successfully carried out for treating metal castings are described in detail below as an aid to persons skilled in the art who may wish to practice the invention.

In all examples the top of the ingot was flat and no shrinkage cavities extended down into the main body of the ingot. Also, the burner was in reusable condition after conclusion of the treatment.

Example 1 A partially covered ingot of stainless steel Weighing 3 tons and having a rectangular top 15 x 28 inches and having a hot-top containing 5 inches depth of metal, in contrast to the conventional 8 inches, was treated with a blow-01f flame for 1 hour while holding a non-watercooled burner nozzle 4 inches from the surface of the metal. The blow-off flame was formed by discharging from the burner nozzle at 500 feet per second a 1.53:1 ratio combustible mixture formed from oxygen and natural gas flowing at 827 and 540 cubic feet per hour, respectively.

Example 2 A partially covered ingot of nickel-molybdenum tool steel weighing 4500 pounds and having a cylindrical top 19 inches in diameter was provided with a hot-top onehalf the depth normally used on such ingots. The ingot then was treated with a blow-01f flame for 1 hour while holding a non-water-cooled burner nozzle 8 /2 inches from the surface of the metal. The blow-01f flame was formed by discharging from the burner nozzle at 500 feet per second a 1.52:1 ratio combustible mixture formed from oxygen and natural gas flowing at 500 and 333 cubic feet per hour, respectively.

Example 3 A partially covered ingot of carbon steel weighing 9000 pounds and having a rectangular top 22 x 25 inches was treatedwith blow-off flames from two nozzles for 65 minutes while holding the two non-water-cooled nozzles 12 inches from the surface of the metal in the hot-top. The blow-0E flames were formed by discharging from both burner nozzles at 500 feet per second a 1.821 ratio combustible mixture formed from oxygen and natural gas flowing at 975 and 540 cubic feet per hour, respectively.

The overall yield of usable steel was 85%, in contrast to 76% obtained without treatment.

Example 4 A partially covered ingot of chromium-moylbdenumvanadium tool steel was poured with a hot-top constituting 7 /z% of the ingot volume, in contrast to 15% in normal practice. The casting then was treated with a cluster of blow-ofl. flames for 14 minutes from a burner nozzle positioned 4 inches above the metal surface. The time was formed by burning a combustible mixture flow- 4 ing at 300 feet per second, and formed from 300 cubic feet per hour of oxygen and 200 cubic feet per hour of natural gas (a 1.521 ratio).

Example 5 An ingot of stainless steel weighing 7360 pounds and having a rectangular top 16 x 31 inches was treated with a blow-off flame for 50 minutes from a burner nozzle positioned 2 /2 inches above the metal surface while leaving the hot-top uncovered. The hot-top had been filled with 390 pounds less metal than usual. The flame was formed by burning a combustible mixture flowing at 500 feet per second, and formed from 1194 and 667 cubic feet per hour, respectively, of oxygen and fuel gas.

Example 6 An ingot of stainless steel weighing 6340 pounds and having a rectangular top 15 x 28 inches was poured with an uncovered hot-top and the surface of the metal was covered with silica. A blow-off flame was then applied to the top of the casting for 50 minutes from a burner nozzle located 3 /2 inches above the top. Oxygen and fuel gas were supplied at 923 and 660 cubic feet per hour, respectively, and the mixture flowed at a velocity of 500 feet per second.

Only 4.1% of the ingot volume contained a pipe, in contrast to the 9% normal pipe.

This application is in part a continuation of my copending application Serial No. 265,942, filed January 11, 1952, now abandoned, and combines therewith the use of slags in combination with the blow-off flame for hottopping, and the oxy-fuel ratios for the use of propane and coke-oven gas and city gas for fuel. I

The slags can be naturally-occurring materials such as Wollastonite or specially prepared synthetics such as dis- The advantages of using slags are: They eliminate depletion of readily oxidizable elements in the steel. They permit heating with higher oxy-fuel gas ratios and thereby take advantage of higher flame temperatures. They permit successful hot-topping of large size ingots.

In treating small size ingots, up to about l5-in. square and depending upon metal chemistry, the primary purpose of the slag is to prevent oxidation of elements which may cause porosity in the hot-top--the major element being carbon. Many alloy steels can be hot-topped using oxy-fuel gas flames in these smaller ingot sizes without requiring slags as barriers.

In hot-topping large size ingots, the problem is completely different. solidification of ingots is expressed as:

T=Ingot solidification time (min.)

K=Co-efficient dependent upon ingot mold characteristics and heating time d=Smallest dimension of ingot (in.)

Using this formula and for simplicity assuming K= 1, the solidification time for a l0-in. square ingot will be 25 min., whereas, this increases to 225 min. for a 30-in. ingot. Large size ingots are exposed, therefore, to the oxidizing influence of the oxy-fuel gas combustion products for a proportionally longer period. Thus, where oxidation would not be a factor on small size ingots of a specific metal chemistry, the problem becomes increasingly ditficult as ingot size increases. For example, x 10 in. ingots of type 304 stainless can easily be heated using oxy-natural gas ratios of 1.5 :1. In heating large size ingots, 22 x 25 in., the oxy-natural gas ratio would have to be reduced to 1.1 :1 to overcome the effect of oxidation by the combustion products. Using this ratio, there is insufficient heat in the combustion products to eifectively hot-top the ingot. The difliculty is caused by the appearance of a powdery slag being formed on the surface of the metal in the hot-top as the heating progresses. This powdery slag probably contains considerable amounts of chromium oxide which is highly refractory. The refractory character of this sl-ag causes considerable heat reflection which substantially decreases the amount of heat made available to the metal in the hot-top. On type 321 stainless, an equally unsatisfactory condition is experienced; however, this slag has a slushy character.

Initial experiments were made introducing crushed glass on the surface of the hot-top prior to the start of heating. This is satisfactory in most cases. Synthetic slags such as those according to Patent No. 2,043,960 are more desirable than crushed glass in instances because of more uniform slag chemistry, control of viscosity, better sizing and ready availability. The disadvantage of synthetic slags is that the cost is higher.

In treating ingots under production conditions, it is desirable in some cases to add exothermic materials to the synthetic slags. The exothermic material imparts heat to the hot-top surface to retard solidification until the teeming ladle is moved sufliciently for the heating tips to be positioned over the ingots.

Timing between the slag addition and the start of heating is important. In treating a 9 x 9 in. ingot, x 200 slag according to Patent No. 2,150,625

Examples I II III IV Percent CaO 29. 5 31. 24 29.18 40.12 Percent MgO 8. 7 11. 01 8. 26 0. 89 Percent 310:... 56. 4 52. 40 57. 48 52. 94 Percent A1203 5. 4 4.11 4. 86 5. 80 Percent F6203 Low 0. 13 0. 24 0.23

Example 7 15 x 28 in., 6350 lb. ingot of type 430 stainless was heating using 928 cu. ft. per hour oxygen and 660 cu. ft. per hour of natural gas and the blowoflf flame technique. The heating time was 50 minutes. Using slags, the top crop was 4.1 percent while for conventional practice ingots, the top crop was 10 percent. Oxy-natural gas hot-topping would not have been possible using this ratio on this ingot size without the use of slag.

Example 8 22 x 25 in., 7000 lb. ingot of type 304 stainless steel was heating using 1640 cu. ft. per hour of oxygen, 480 cu. ft. per hour of propane, glass slag and blowotf flame. Ingot yield was 88 percent including top crop, bottom crop and scale loss. The regular cast ingot made for comparative purposes showed a yield of 80 percent.

6 Again, this ingot could not have been hot-topped without the use of the slag.

When using propane, coke-oven and city gas, the ranges of the oxy-fuel gas ratios are:

Gray-Propane 2.5: 1 to 4.0: Qxy-Co'ke oven and city gas 1 to 1.1:

What is claimed is:

1. In the process of treating a freshly poured molten metal casting to keep the top of the casting molten while said casting solidifies from the bottom to the top thereof to reduce the size of the shrinkage cavity therein, wherein an oxy-fuel flame is directed against the top surface of said casting during such cooling, the improvement which comprises in combination therewith positioning a burner nozzle above the top surface of said casting and vertically spaced therefrom a distance such that overheating of the nozzle is avoided, and applying from said burner nozzle against said top surface an oxy-fuel gas mixture having an oxygen to fuel gas ratio of from 1.3:1 to 1.8:1 and a velocity of from 200 feet per second to 1000 feet per second, to burn said mixture with a stable blow-01f flame by continuous ignition thereof by the molten casting.

2. In the process of treating a freshly poured molten metal casting to keep the top of the casting molten while said casting solidifies from the bottom to the top thereof to reduce the size of the shrinkage cavity therein, wherein an oxy-fuel flame is directed against the top surface of said casting during such cooling, the improvement which comprises in combination therewith positioning a burner nozzle above the top surface of said casting and vertically spaced therefrom a distance such that overheating of the nozzle is avoided, and applying from said burner nozzle against said top surface an oxy-fuel gas mixture having an oxygen-to-fuel gas ratio of from 1.321 to 1.811 for natural gas, 2.5:1 to 4.0:1 for propane and 05:1 to 1.1:1 for coke oven and city gas and a velocity of from 200 feet per second to 1000 feet per second, to burn said mixture with a stable blow-off flame by continuous ignition thereof by the molten casting.

3. In the process of treating a freshly poured molten metal casting to keep the top of the casting molten while said casting solidifies from the bottom to the top thereof to reduce the size of the shrinkage cavity therein, wherein an oxy-fuel flame is directed against the top surface of said casting during such cooling, the improvement which comprises in combination therewith introducing slag on the surface of the hot-top to overcome the effect of oxidation by the combustion products and prevent reflection by refractory oxides, positioning a burner nozzle above the top surface of said casting and vertically spaced therefrom a distance such that overheating of the nozzle is avoided, and applying from said burner nozzle against said top surface an oxy-fuel gas mixture having an oxygen-tofuel gas ratio of from 1.311 to 1.8:1 for natural gas, 2.5:1 to 4.021 for propane and 0.5 :1 to 1.121 for coke oven and city gas and a velocity of from 200 feet per second to 1000 feet per second, to burn said mixture with a stable blow-off flame by continuous ignition thereof by the molten casting.

References Cited in the file of this patent UNITED STATES PATENTS 359,974 Irwin Mar. 22, 1887 1,310,072 Hadfield July 15, 1919 1,336,234 Jamison Apr. 6, 1920 1,671,253 Parsons et al May 29, 1928 1,763,047 Hepburn June 10, 1930 1,874,341 Osthofl Aug. 30, 1932 1,986,201 Huff Jan. 1, 1935 2,116,096 Caldwell May 3, 1938 2,116,671 Trofimov July 18, 1939 2,353,657 Edwards et al. July 18, 1944 2,638,159 Winkelman May 12, 1,953 

1. IN THE PROCESS OF TREATING A FRESHLY POURED MOLTEN METAL CASTING TO KEEP THE TOP OF THE CASTING MOLTEN WHILE SAID CASTING SOLIDFIES FROM THE BOTTOM TO THE TOP THEREOF TO REDUCE THE SIZE OF THE SHRINKAGE CAVITY THEREIN, WHEREIN AN OXY-FUEL FLAME IS DIRECTED AGAINST THE TOP SURFACE OF SAID CASTING DURING SUCH COOLING, THE IMPROVEMENT WHICH COMPRISES IN COMBINATION THEREWITH POSITIONING A BURNER NOZZLE ABOVE THE TOP SURFACE OF SAID CASTING AND VERTICALLY SPACED THEREFROM A DISTANCE SUCH THAT OVERHEATING OF THE NOZZLE IS AVOIDED, AND APPLYING FROM SAID BURNER NOZZLE AGAINST SAID TOP SURFACE AN OXY-FUEL GAS MIXTURE HAVING AN OXYGEN TO FUEL GAS RATIO OF FROM 1.3:1 TO 1.8:1 AND A VELOCITY OF FROM 200 FEET PER SECOND TO 1000 FEET PER SECOND, TO BURN SAID MIXTURE WITH A STABLE BLOW-OFF FLAME BY CONTINUOUS IGNITION THEREOF BY THE MOLTEN CASTING. 